Drawing graphs without labels
On FRQs, graph parts are scored on whether axes, curves, and points are correctly labeled. A perfectly shaped cost curve with no axis labels earns zero for that part. Always label before moving on.
Applying perfect competition rules to monopoly
In perfect competition, P = MR. In monopoly, P is greater than MR because the firm faces a downward-sloping demand curve. Using P = MR to find monopoly output is one of the most common errors on both MCQ and FRQ.
Confusing shifts with movements along a curve
A change in price causes a movement along the demand curve. A change in income, preferences, or related goods prices causes a shift of the curve. MCQ traps frequently hinge on this distinction.
Ignoring the short-run versus long-run distinction
In the short run, a firm may operate at a loss if P is above AVC. In the long run, firms enter or exit until economic profit equals zero. Mixing up these timeframes leads to wrong answers on shutdown, entry, and efficiency questions.
Running out of time on the long FRQ
Students who do not budget time during the reading period often spend 35-40 minutes on Question 1 and rush or skip Questions 2 and 3. Since Q2 and Q3 together equal Q1 in total points, leaving them incomplete is a costly error.